This invention relates to improvements collapsible steering column assemblies for vehicles to permit collapse during a crash.
Steering column assemblies for automotive vehicles and the like are increasingly required to be adjustable for steering wheel height known as rake and, in many cases, steering wheel distance known as reach. This requires the column shroud, within which the steering column shaft attached to the steering wheel is rotatably located, to be fixed to the vehicle by a clamp mechanism which can be locked and unlocked to either prevent or permit adjustment of the column shroud position respectively.
A typical adjustable steering column assembly comprises a first shroud portion, a second shroud portion and a clamp mechanism that includes a bracket secured to a fixed part of a vehicle and in which the first and second portions are releasably engaged by the clamp mechanism to selectively permit an amount of relative movement between the first and second portions that is required during adjustment of the steering column assembly. The clamp mechanism can be unlocked and locked by movement of a locking lever or handle or, sometimes, electrically using a motor or perhaps hydraulically or pneumatically.
By releasing the clamp mechanism and telescopically sliding the first portion over the second portion the length of the shroud can be altered, altering the reach position of an associated steering wheel. By moving both portions together up and down relative to the clamp mechanism the rake can be adjusted. In some assemblies only one of reach and rake may be adjusted. The clamp mechanism may clamp the shroud to a bracket (known as a support bracket) which is connected to the vehicle. Thus, when the clamp mechanism is locked the length of the steering column assembly is fixed, and it is prevented from moving due to the rigid connection through the bracket to the vehicle.
In a known arrangement the clamp mechanism comprises a relatively long clamp bolt having a head or nut at each end, a cam mechanism that is threaded onto the clamp bolt, and a locking lever or handle that operates the cam mechanism to vary the length of the cam mechanism. A part of the support bracket and/or shroud is also threaded onto the bolt, and as the cam mechanism increases in length the support bracket and shroud are squeezed together to clamp them in place. The lever must rotate relatively freely around the clamp bolt and yet should not rock excessively which give an unsatisfactory feel to the operator. In the past, this has been achieved using tight tolerances between the parts, but this has not always been satisfactory.